In blasting applications, e.g., surface mining, underground mining, quarrying, civil construction, and/or seismic exploration on land or in the ocean, explosives are buried, e.g., in boreholes in selected patterns. To initiate the buried explosives, various initiation apparatuses are used, e.g., detonating cord (also known as “det cord”), or electrically controlled detonators. The timing of the blasts of the explosives in different locations in a blasting pattern can be critical to the success of a blasting operation.
In some environments and complicated applications, it may be undesirable to connect buried explosives with physical connectors, e.g., det cord or electrical cables. For example, such connectors can cause problems if they are strung across a mining site.
Wireless communication with electronic detonators has been proposed, but existing systems remain inappropriate for some applications. For example, some proposed wireless systems using radio-frequency (RF) signals require a line-of-sight connection from a blasting machine to the collar of each borehole. Furthermore, being able to activate electronic detonators with wireless signals may make storing, transporting and deploying such detonators extremely dangerous if blasting signals are received and interpreted at the wrong time, or incorrectly interpreted.
A first class of wireless electronic blasting systems may employ conventional radio wave communications to and from the borehole. In these systems, the receiver or transceiver at each borehole has at least an antenna outside the borehole to communicate, since radio waves may not travel through rock or even through stemming material. A secondary communication channel may be needed between the “top box” and the in-hole device in which the timing is done and which, at the correct time, will cause initiation of the explosives train in the borehole.
A second class of wireless electronic blasting systems may employ through-the-rock wireless communication, in which communication is effected via generation over the blast pattern of a controlled magnetic field that is detected by magnetometers which are part of the initiation devices within each borehole.
Initiation that relies on radio communication to (and optionally from) each borehole has the disadvantage of requiring access by the radio waves to the receiver at the collar of the borehole at blasting time. Since line-of-sight communication is generally much more reliable, it is generally much preferred to reliance on wave reflection or refraction for communication at blasting time. In underground mining in particular, preservation of line-of-sight communication from the firing transmitter to each receiver at the borehole collar is sometimes difficult and may be impossible (for example due to unsafe ground conditions). Through-the-rock communication—which may be referred to as “through-the-earth” (TTE) communication—may be advantageous in allowing blasting to proceed when access to the collars of the holes to be blasted may not be convenient, or safe, or even possible.
The through-rock wireless systems that have been described include a detonator. In these systems, the magnetically-transmitted commands are received by the receiver devices in each borehole. The receiver device then sends an appropriate command to an electric or electronic detonator, which functions as the first element in a conventional explosives train. A disadvantage of this system is inclusion of the detonator which must either be factory or field assembled with the receiver device. Detonators generally contain primary explosives which are more sensitive to electromagnetic interference (EMI), heat, friction, spark and impact, in both manufacture and use, than secondary explosives. For example, a fusehead may pick up an electromagnetic (EM) signal as it generally has poor EM protection, even if electronic portions of a detonator are EM protected. Detonators may require special handling, transportation and storage, which adds to the inconvenience and cost of using detonators as essential components.
Laser initiation systems for blasting may use a laser outside a borehole, and an optical fibre for guiding energy to an explosive in the borehole, or a diode laser included with control electronics connected into the borehole; however, existing laser systems require electrical or optical connections from the initiating device out of the borehole, and are thus prone to failure in some applications, e.g., where the material surrounding the initiating device moves before firing (e.g., due to other earlier blasts in the same area), and may contribute undesirable wire or cable waste in a blasting site.
There is a need, at least in some applications, to simplify electronic blasting systems and to improve their safety.
It is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative.